U.S. patent application number 13/462889 was filed with the patent office on 2012-08-30 for solid-state imaging device.
This patent application is currently assigned to PANASONIC CORPORATION. Invention is credited to YUTAKA HIROSE, YOSHIHISA KATO, MITSUYOSHI MORI, TORU OKINO.
Application Number | 20120217494 13/462889 |
Document ID | / |
Family ID | 43969718 |
Filed Date | 2012-08-30 |
United States Patent
Application |
20120217494 |
Kind Code |
A1 |
OKINO; TORU ; et
al. |
August 30, 2012 |
SOLID-STATE IMAGING DEVICE
Abstract
Solid-state imaging device of the present invention is a
backside-illumination-type solid-state imaging device including
wiring layer formed on first surface side of semiconductor
substrate; and light receiving section that photoelectrically
converts light incident from second surface side that is opposite
from first surface side, wherein spontaneous polarization film
formed of a material having spontaneous polarization is formed on a
light receiving surface of light receiving section. Accordingly, a
hole accumulation layer can be formed on the light receiving
surface of light receiving section, and a dark current can be
suppressed.
Inventors: |
OKINO; TORU; (Osaka, JP)
; KATO; YOSHIHISA; (Shiga, JP) ; HIROSE;
YUTAKA; (Kyoto, JP) ; MORI; MITSUYOSHI;
(Kyoto, JP) |
Assignee: |
PANASONIC CORPORATION
Osaka
JP
|
Family ID: |
43969718 |
Appl. No.: |
13/462889 |
Filed: |
May 3, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2010/004921 |
Aug 5, 2010 |
|
|
|
13462889 |
|
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Current U.S.
Class: |
257/43 ; 257/432;
257/E31.015; 257/E31.127 |
Current CPC
Class: |
H01L 27/14665 20130101;
H01L 27/1464 20130101; H01L 27/14685 20130101; H01L 27/14625
20130101 |
Class at
Publication: |
257/43 ; 257/432;
257/E31.127; 257/E31.015 |
International
Class: |
H01L 31/0296 20060101
H01L031/0296; H01L 31/0232 20060101 H01L031/0232 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 5, 2009 |
JP |
2009-254404 |
Claims
1. A solid-state imaging device of a backside-illumination type
comprising: a wiring layer formed on a first surface of a
semiconductor substrate; and a light receiving section that
photoelectrically converts light incident from a second surface of
the semiconductor substrate that is opposite from the first
surface, wherein a spontaneous polarization film formed of a
material having spontaneous polarization is formed on the second
surface.
2. The solid-state imaging device according to claim 1, wherein a
direction of polarization of the spontaneous polarization film is a
direction from the first surface to the second surface.
3. The solid-state imaging device according to claim 1, wherein the
spontaneous polarization film is of a material in which a crystal
is oriented.
4. The solid-state imaging device according to claim 3, wherein the
material in which the crystal is oriented is any one selected from
ZnO, GaN, AlN, SrTiO.sub.3, Pb(Zr, Ti)O.sub.3,
SrBi.sub.2Ta.sub.2O.sub.9, (Bi, La).sub.4Ti.sub.3O.sub.12,
BaTiO.sub.3, BiFeO.sub.3, and Ba.sub.xSr.sub.(1-x)TiO.sub.3.
5. The solid-state imaging device according to claim 3, wherein the
material in which the crystal is oriented is formed at a deposition
temperature of 400.degree. C. or less.
6. The solid-state imaging device according to claim 3, wherein the
material in which the crystal is oriented is ZnO, and conductivity
type of the ZnO is p-type.
7. The solid-state imaging device according to claim 3, wherein the
material in which the crystal is oriented is ZnO, and an oxygen
defect concentration of the ZnO is 1.times.10.sup.17
(piece/cm.sup.3) or less.
8. The solid-state imaging device according to claim 1, wherein the
spontaneous polarization film is made of an organic material having
polarization, and polarized charges of the organic material are
generated in a direction of film growth of the organic material by
an orientation of the organic material.
9. The solid-state imaging device according to claim 8, wherein the
spontaneous polarization film is a fluoropolymer.
10. The solid-state imaging device of any one according to claim 1,
wherein the spontaneous polarization film is covered by a hydrogen
barrier film.
11. The solid-state imaging device of any one according to claim 1,
wherein the spontaneous polarization film is sandwiched by hydrogen
barrier films.
12. The solid-state imaging device of any one according to claim 1,
wherein the spontaneous polarization film is formed of two or more
layers of spontaneous polarization films being laminated.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present invention relates to a solid-state imaging
device in which a plurality of light receiving sections made of pn
photodiodes and the like are formed on a semiconductor substrate,
and particularly relates to a backside-illumination-type
solid-state imaging device having a wiring layer formed on one
surface of a semiconductor substrate and a light receiving section
that photoelectrically converts light incident from the other
surface of the semiconductor substrate.
[0003] 2. Background Art
[0004] In recent years, high quality and compactness are desired
for a solid-state imaging device, and pixel size reduction is
frequently adapted. However, the pixel size reduction has physical
limitations, and there is an occurring problem that an area of a
photodiode for converting light into electric signals must be made
smaller as the pixel size becomes smaller, and sensitivity to light
diminishes.
[0005] In a typical solid-state imaging device, a wiring for
outputting the signals converted in each photodiode to outside is
formed on a semiconductor substrate on which a plurality of
photodiodes are formed. Since light is made incident from a side of
the surface on which the wiring of the solid-state imaging device
is formed, light is collected by using a microlens and the like so
that the incident light can pass though the wiring. However, when
the wiring becomes complicated and becomes a multilayer wiring,
even if the light is collected by the microlens, vignetting of the
incident light occurs due to obstacles such as the wiring, and it
becomes impossible to obtain sufficient sensitivity.
[0006] Thus, recently, a backside-illumination-type solid-state
imaging device that injects the light from a surface on an opposite
side of a surface onto which a wiring is formed is proposed. With
the backside-illumination-type structure, it is possible to make an
aperture ratio of each pixel ideally at 100%, and the sensitivity
can be maintained even if the pixel size is reduced. However, since
the backside-illumination-type solid-state imaging device is
configured to inject the light from the surface on the opposite
side of the surface onto which the wiring is formed, in order to
manufacture the backside-illumination-type solid-state imaging
device, a special manufacturing process is necessary for thinning a
thickness of the semiconductor substrate onto which the light
receiving sections are formed.
[0007] As a method of manufacturing the backside-illumination-type
solid-state imaging device, typically, a method that uses an SOI
(Silicon On Insulator) substrate is known, in which after having
formed respective layers such as the light receiving sections, the
wiring, and the like on the SOI substrate, a supporting substrate
is bonded thereto, and the silicon substrate on a back surface side
of the supporting substrate is removed. However, in removing the
silicon substrate, damage is applied to light receiving sections,
and defect levels of a substrate interface are generated in the
light receiving sections by this damage. In this case, there had
been a problem that, even if the solid-state imaging device is in a
darkened state (a state in which no signal charge is present that
is to be photoelectrically converted in the light receiving
sections), charges are detected by the defect levels of the
substrate interface in the light receiving sections, and the dark
current (noise current) is generated. Accordingly, even if the
sensitivity to the incident light is increased by employing the
backside-illumination-type solid-state imaging device, whereas on
the other hand if the dark current increases, it practically
becomes impossible to use it as the solid-state imaging device.
[0008] Conventionally, techniques to prevent this dark current have
been proposed (refer to Unexamined Japanese Patent Publication No.
114-38872, Unexamined Japanese Patent Publication No. 2008-306154,
and Unexamined Japanese Patent Publication No. 2008-306160).
Hereinbelow, two conventional techniques for preventing the dark
current will be described with reference to the drawings.
[0009] FIG. 8 is a cross-sectional view of a solid-state imaging
device of a first conventional technique disclosed in Unexamined
Japanese Patent Publication No. 114-38872.
[0010] As shown in FIG. 8, solid-state imaging device 800 of the
first conventional technique includes p-type semiconductor
substrate 801, first n-type semiconductor layer 802 and second
n-type semiconductor layer 803 formed on p-type semiconductor
substrate 801, p-type semiconductor layers 804 formed on p-type
semiconductor substrate 801, silicon oxide film 805 formed on first
n-type semiconductor layer 802, second n-type semiconductor layer
803, and p-type semiconductor layers 804, and gate electrode 806
formed on silicon oxide film 805 above second n-type semiconductor
layer 803 and p-type semiconductor layer 804.
[0011] Further, in solid-state imaging device 800 of the first
conventional technique, negative fixed charges are embedded by
implanting aluminum ions into silicon oxide film 805, whereby
negative charge region 807 is formed. That is, negative charge
region 807 as a hole accumulation layer is formed by bringing up a
surface potential of p-type semiconductor substrate 801. In this
way, the solid-state imaging device of the first conventional
technique configures an insulation film interface between p-type
semiconductor substrate 801 and silicon oxide film 805 to be
non-depleted by forming the hole accumulation layer, and thereby
electrons generated at an interface level is suppressed, and an
occurrence of dark current is prevented.
[0012] Next, solid-state imaging devices of a second conventional
technique disclosed in Unexamined Japanese Patent Publication No.
2008-306154, Unexamined Japanese Patent Publication No. 2008-306160
will be described.
[0013] FIG. 9 is a cross-sectional view of solid-state imaging
device 900 of the second conventional technique.
[0014] Solid-state imaging device 900 of the second conventional
technique is a backside-illumination-type solid-state imaging
device, and as shown in FIG. 9, includes semiconductor substrate
901, and light receiving section 902 and peripheral circuit section
903 formed on semiconductor substrate 901. Film 904 that lowers an
interface level and film 905 including negative fixed charges are
formed on light receiving section 902. Insulation film 906 is
formed on film 905 including the negative fixed charges, and
light-shielding film 907 is formed on insulation film 906 above
peripheral circuit section 903. Further, insulation film 908 having
transparency to incident light is formed on film 905 having the
negative fixed charges above light receiving section 902. Further,
color filter layer 909 and light condensing lens 910 are formed on
insulation film 908.
[0015] In solid-state imaging device 900 of the second conventional
technique, since film 905 including the negative fixed charges is
formed on film 904 that lowers the interface level, hole
accumulation layer 911 is formed on a light receiving surface side
of light receiving section 902 due to an electric field caused by
the negative fixed charges. Accordingly, the generation of the
charges from the interface is suppressed, and the dark current
caused due to the interface level can be suppressed.
[0016] As described above, solid-state imaging device 800 of the
first conventional technique and solid-state imaging device 900 of
the second conventional technique form the hole accumulation layer
by using the negative fixed charges, and thereby suppress the dark
current caused by the interface level.
SUMMARY
[0017] However, in solid-state imaging device 800 of the first
conventional technique, since the negative fixed charges are
embedded into the insulation film by implanting aluminum ions, an
additional manufacturing process for implanting aluminum ions is
required. In addition, in this additional manufacturing process,
aluminum ions need to be implanted with high energy, and there is a
problem that this manufacturing process damages the
photodiodes.
[0018] Further, in solid-state imaging device 900 of the second
conventional technique in which film 905 including negative fixed
charges is formed, although there is no damage to the photodiodes
due to the implantation of aluminum ions as in the first
conventional technique, the hole accumulation layer is formed by
the electric field caused by the negative fixed charges. Since the
amount of the negative fixed charges greatly change depending on a
level caused by an interface in the insulation film and between the
insulation film and the light receiving section, it is very
difficult to control the electric field for sufficiently forming
the hole accumulation layer by the film including negative fixed
charges.
[0019] Further, since the negative fixed charges are prone to
disappear by manufacturing processes such as moisture treatment and
heat treatment, it is also difficult to control the amount of the
negative fixed charges for forming the hole accumulation layer.
[0020] As described above, since difficult controls accompany the
film including negative fixed charges, even if the hole
accumulation layer can be formed sufficiently in a particular pixel
region, there may be cases in which the hole accumulation layer
cannot be formed sufficiently in other pixel regions. Accordingly,
a property variation among pixels becomes large, and there is a
problem that a sufficient property as a solid-state imaging device
cannot be achieved.
[0021] The present invention has been made in view of the above
problems, and aims to provide a backside-illumination-type
solid-state imaging device that is capable of controlling the dark
current caused by the interface level by forming a hole
accumulation layer on a light receiving surface of the light
receiving section uniformly without any variation among pixels.
[0022] An aspect of the solid-state imaging device of the present
invention is a solid-state imaging device of a
backside-illumination type including: a wiring layer formed on a
first surface side of a semiconductor substrate; and a light
receiving section that photoelectrically converts light incident
from a second surface side that is opposite from the first surface
side, wherein a spontaneous polarization film formed of a material
having spontaneous polarization is formed on a light receiving
surface of the light receiving section.
[0023] With this configuration, by the spontaneous polarization of
the spontaneous polarization film, the hole accumulation layer can
be easily formed on the light receiving surface of the light
receiving section uniformly without any variation among pixels.
Thus, the dark current by the charges caused by the interface level
of the light receiving section can be controlled uniformly over an
entirety of the imaging region.
[0024] Further, according to the aspect of the solid-state imaging
device of the present invention, a direction of polarization of the
spontaneous polarization film is preferably a direction from the
first surface to the second surface.
[0025] With this configuration, the negative charges can be
provided on the light receiving surface side of the spontaneous
polarization film, so that the hole accumulation layer can be
formed in an interface on the light receiving surface of the light
receiving section uniformly without any variation among pixels.
[0026] Further, according to the aspect of the solid-state imaging
device of the present invention, the spontaneous polarization film
is preferably of a material in which a crystal is oriented.
[0027] With this configuration, the polarization can be generated
by the crystal orientation of the spontaneous polarization film, so
that an influence of manufacturing processes such as water
treatment and heat treatment can be eliminated. Thus, since a
change by the manufacturing processes for the negative fixed
charges can be almost eliminated, the hole accumulation layer can
further be formed uniformly without any variation among pixels.
[0028] Further, according to the aspect of the solid-state imaging
device of the present invention, the material in which the crystal
is oriented is any one selected from ZnO, GaN, AlN, SrTiO.sub.3,
Pb(Zr, Ti)O.sub.3, SrBi.sub.2Ta.sub.2O.sub.9, (Bi,
La).sub.4Ti.sub.3O.sub.12, BaTiO.sub.3, BiFeO.sub.3, and
Ba.sub.xSr.sub.(1-x)TiO.sub.3.
[0029] With this configuration, since an amount of the spontaneous
polarization of the spontaneous polarization film can be increased,
a sufficient hole accumulation layer can further be formed on the
light receiving surface, and it becomes possible to effectively
suppress the dark current.
[0030] Further, according to the aspect of the solid-state imaging
device of the present invention, the material in which the crystal
is oriented is preferably formed at a deposition temperature of
400.degree. C. or less.
[0031] Accordingly, the deposition of the spontaneous polarization
film can be performed even after having formed the wirings, and the
manufacturing process can be simplified.
[0032] Further, according to the aspect of the solid-state imaging
device of the present invention, the material in which the crystal
is oriented is preferably ZnO, and conductivity type of the ZnO is
preferably p-type.
[0033] Accordingly, it becomes easier to form the hole accumulation
layer by a band structure of the ZnO film and the semiconductor
substrate on which the ZnO film is formed, and effectively suppress
the dark current.
[0034] Further, according to the aspect of the solid-state imaging
device of the present invention, the material in which the crystal
is oriented is preferably ZnO, and an oxygen defect concentration
of the ZnO is preferably 1.times.10.sup.17 (piece/cm.sup.3) or
less.
[0035] Accordingly, it becomes easier to form the hole accumulation
layer by the band structure of the ZnO film and the semiconductor
substrate on which the ZnO film is formed, and effectively suppress
the dark current.
[0036] Further, according to the aspect of the solid-state imaging
device of the present invention, the spontaneous polarization film
is preferably made of an organic material having polarization, and
polarized charges of the organic material are preferably generated
in a direction of film growth of the organic material by an
orientation of the organic material.
[0037] With this configuration, since the spontaneous polarization
film can be formed by the low-temperature manufacturing process,
the amount of the spontaneous polarization can be increased.
[0038] Further, according to the aspect of the solid-state imaging
device of the present invention, the spontaneous polarization film
is preferably a fluoropolymer.
[0039] With this configuration, since the spontaneous polarization
film can be formed from a low molecular material made of a low
molecular mass body, deposition using a vacuum deposition method or
the like by which the control of the film thickness and orientation
can be performed relatively easily becomes possible.
[0040] Further, according to the aspect of the solid-state imaging
device of the present invention, the spontaneous polarization film
is preferably covered by a hydrogen barrier film.
[0041] With this configuration, intrusion of hydrogen that
deteriorates spontaneous polarization property of the spontaneous
polarization film can be suppressed. Thus, in a manufacturing
process such as water treatment and hydrogen annealing, the
deterioration of the spontaneous polarization property of the
spontaneous polarization film can be suppressed, and a sufficient
hole accumulation layer can be formed on the light receiving
surface.
[0042] Further, according to the aspect of the solid-state imaging
device of the present invention, the spontaneous polarization film
is preferably sandwiched by hydrogen barrier films.
[0043] Accordingly, the deterioration of the spontaneous
polarization property of the spontaneous polarization film can be
suppressed.
[0044] Further, according to the aspect of the solid-state imaging
device of the present invention, the spontaneous polarization film
is preferably formed of two or more layers of spontaneous
polarization films being laminated.
[0045] With this configuration, compared to a case of forming the
spontaneous polarization film with a single layer, a region in
which the hole accumulation layer cannot be formed sufficiently due
to an interface of grains formed by the spontaneous polarization
film is reduced; and further, the hole accumulation layer can be
formed uniformly without any variation among pixels
[0046] According to the solid-state imaging device of the present
invention, the hole accumulation layer can be formed on the light
receiving surface of the light receiving section uniformly without
any variation between pixels. Thus, the dark current caused by the
interface level can effectively be suppressed.
BRIEF DESCRIPTION OF DRAWINGS
[0047] FIG. 1 is a diagram showing a circuit configuration of a
solid-state imaging device of a first exemplary embodiment of the
present invention.
[0048] FIG. 2 is a diagram schematically showing a cross section of
pixels in the solid-state imaging device of the first exemplary
embodiment of the present invention.
[0049] FIG. 3 is a diagram schematically showing a cross section of
pixels in a solid-state imaging device of a modification of the
first exemplary embodiment of the present invention.
[0050] FIG. 4 is a diagram schematically showing a crystal
structure of ZnO.
[0051] FIG. 5 is a diagram schematically showing a molecular chain
structure of a PVDF.
[0052] FIG. 6 is a diagram schematically showing a cross section of
pixels in a solid-state imaging device of a second exemplary
embodiment of the present invention.
[0053] FIG. 7 is a diagram schematically showing a cross section of
pixels in a solid-state imaging device of a third exemplary
embodiment of the present invention.
[0054] FIG. 8 is a cross-sectional view of a solid-state imaging
device of a first conventional technique.
[0055] FIG. 9 is a cross-sectional view of a solid-state imaging
device of a second conventional technique.
DESCRIPTION OF EMBODIMENTS
[0056] Hereinbelow, a solid-state imaging device of embodiments of
the present invention will be described with reference to the
drawings.
FIRST EXEMPLARY EMBODIMENT
[0057] FIG. 1 is a diagram showing a circuit configuration of
solid-state imaging device 100 of a first exemplary embodiment of
the present invention.
[0058] As shown in FIG. 1, solid-state imaging device 100 of the
first exemplary embodiment of the present invention includes
imaging region 102 in which a plurality of pixels 101 are arranged
in a matrix, vertical shift register 103 for selecting pixel 101,
and horizontal shift register 105 that transmits a signal outputted
from pixel 101 through output signal line 104.
[0059] Pixel 101 is made of photoelectric conversion element 106
that is for example a photodiode, transfer transistor 107 that
transfers charges generated in photoelectric conversion section 106
to a floating diffusion section (FD section), amplifying transistor
108 that amplifies a charge signal stored in the FD section and
outputs the amplified charge signal to output signal line 104,
resetting transistor 110 that has one end connected to power
voltage supplying section 109 and resets a state of the FD section,
and selecting transistor 111 that controls whether or not to output
the signal that is amplified by amplifying transistor 108 to output
signal line 104. A gate electrode of transfer transistor 107, a
gate electrode of resetting transistor 110 and a gate electrode of
selecting transistor 111 are respectively connected to their
corresponding output pulse lines 112, 113, 114 that are
respectively controlled by vertical shift register 103.
[0060] Note that, the above configuration of pixels 101 is merely
an example, and a circuit configuration can be adapted to the
solid-state imaging device of the present invention so long as one
or more photoelectric conversion elements 106 are arranged within
each pixel 101. Further, by adapting the structure of photoelectric
conversion elements 106 of the present embodiment to a MOS type
solid-state imaging device, it is possible to provide peripheral
circuits (vertical shift register 103, horizontal shift register
105, signal output circuit, column amplifier and the like) on the
same chip as imaging region 102. In this case, reduction of area
and shortening a signal processing time and the like can be
achieved. Further, it is also possible to adapt the structure of
photoelectric conversion elements 106 of the present embodiment to
a CCD type solid-state imaging device.
[0061] FIG. 2 is a diagram schematically showing a cross section of
pixels 101 in solid-state imaging device 100 of the first exemplary
embodiment of the present invention. The solid-state imaging device
of the present embodiment is a backside-illumination-type
solid-state imaging device, and has a structure in which light is
made incident from an opposite surface from a surface on which the
wiring layer is formed.
[0062] As shown in FIG. 2, solid-state imaging device 100 of the
first exemplary embodiment of the present invention includes
semiconductor substrate 201, light receiving sections 202 formed of
pn photodiodes formed on semiconductor substrate 201, wiring layer
203 formed on first surface 201a (front surface) of semiconductor
substrate 201, and spontaneous polarization film 204 formed at
least on a light receiving surface side of light receiving sections
202 on semiconductor substrate 201. Further, element isolation
sections 205 that separate light receiving sections 202 are formed
in semiconductor substrate 201. On an opposite side of the side
from which the light is incident of wiring layer 203, supporting
substrate 206 formed of a silicon substrate or glass substrate is
provided.
[0063] In the present embodiment, light receiving sections 202 are
formed corresponding to respective pixels 101 of imaging region 102
shown in FIG.
[0064] 1; and they photoelectrically convert the light incident
(incident light) from second surface 201b (back surface) that is
the opposite side surface of first surface 201a of semiconductor
substrate 201. Light receiving sections 202 output pixel signals
based on the charges generated according to a light receiving
amount of the incident light. Light receiving sections 202 can be
configured for example by forming pn junctions on the semiconductor
substrate. Specifically, n-type silicon substrate is used as
semiconductor substrate 201, a p-type semiconductor well region is
formed on the n-type silicon substrate, and n-type semiconductor
regions are formed on the p-type semiconductor well region, whereby
the pn photodiodes are formed.
[0065] Wiring layer 203 is made of a plurality of wirings 207a,
207b for outputting the pixel signals generated in light receiving
sections 202 to outside and the like, and interlayer insulating
film 208 for insulating the plurality of wirings 207a, 207b.
Wirings 207a, 207b are for example made of aluminum wirings formed
of aluminum. Note that, although wirings 207a, 207b are formed in a
two-layer structure in the solid-state imaging device shown in FIG.
2, the configuration thereof is not limited to this. For example,
wirings 207a, 207b may be formed as a multiple-layer wiring
structure in which three or more plural types of wirings are
laminated in two or more layers. In the present embodiment, for
example, output signal line 104 or output pulse lines 112, 113, 114
shown in FIG. 1 may be formed as wirings with the multiple-layer
wiring structure.
[0066] Spontaneous polarization film 204 is formed on the light
receiving surface of light receiving sections 202, and in the
present embodiment, it is formed on a second surface 201b side of
semiconductor substrate 201 that is the light receiving surface
side of light receiving sections 202. This spontaneous polarization
film 204 is a film having spontaneous polarization, and is made of
a material having an electric dipole in which centers of balance of
positive and negative charges spontaneously separate. If light
receiving sections 202 are the pn photodiodes in the case of using
the n-type silicon substrate, spontaneous polarization film 204 is
polarized so that the light incident side of spontaneous
polarization film 204 is positive and light receiving section 202
side is negative. Accordingly, holes are induced to an interface on
the light receiving surface side of light receiving sections 202
(n-type semiconductor region), and the hole accumulation layer is
formed.
[0067] In the present embodiment, backside-illumination-type
solid-state imaging device 100 is manufactured using an SOI
substrate provided by forming a silicon substrate on an insulation
film on a substrate. In this case, light receiving sections 202 and
wiring layer 203 are formed on the silicon substrate on the
insulation film of the SOI substrate, supporting substrate 206
formed of silicon substrate is bonded on wiring layer 203, and
thereafter the other substrate of the SOI substrate is removed. The
removal of the other substrate can be performed by dry etching or
wet etching with the insulation film of the SOI substrate as an
etching stopper layer, or physical polishing. Note that, although
the method of using the SOI substrate has been described as a mere
example, manufacture by using a conventional substrate instead of
using the SOI substrate is also possible.
[0068] Further, in the present embodiment, although the silicon
substrate is used as supporting substrate 206, a glass substrate
can also be used as supporting substrate 206. Note that, supporting
substrate 206 is not limited to the silicon substrate or the glass
substrate. Supporting substrate 206 can be replaced with any
material so long as it is capable of maintaining strength of a
substrate with respect to handling in the event where the substrate
onto which devices such as the light receiving sections are formed
becomes thin.
[0069] As described above, a step of removing the substrate in
order to use the SOI substrate becomes required to manufacture the
backside-illumination-type solid-state imaging device. In this step
of removing the substrate, since the physical polishing, dry
etching, wet etching and the like will be performed, the surface of
the light receiving sections on which the light is incident is
damaged in a way which would not occur in a
frontside-illumination-type solid-state imaging device.
Accordingly, in the light receiving sections, an interface level
caused by the damage in the step of removing the substrate is
present, and the dark current is generated thereby.
[0070] Contrary to this, solid-state imaging device 100 of the
first exemplary embodiment of the present invention, since
spontaneous polarization film 204 is formed on the side of the
surface of light receiving sections 202 on which the light is
incident, the hole accumulation layer can be formed on the side of
the surface of light receiving sections 202 on which the light is
incident by the spontaneous polarization of spontaneous
polarization film 204. Accordingly, noise charges generated in the
interface level can be reduced, and the dark current can be
suppressed. Moreover, since spontaneous polarization film 204 can
easily be deposited uniformly with respect to the respective
pixels, the spontaneous polarization film having the same
spontaneous polarization with respect to the light receiving
section of each pixel can be formed. Thus, since the hole
accumulation layer can be formed on the light receiving section
uniformly without any variation among the pixels, the dark current
of the entirety of the imaging region can be suppressed
effectively.
[0071] Note that, FIG. 2 is depicted to exemplify only the
characteristic configuration of the solid-state imaging device of
the present embodiment, so that other configurations such as color
filters and microlens are omitted. Further, the shapes of the
configuration shown in FIG. 2 are not limited to this; in a
backside-illumination-type solid-state imaging device having the
configuration to receive the light incident from the surface
opposite from the surface from which the substrate is removed and
on which the wiring layer is formed, similar effect to that
described above can be achieved.
[0072] Further, in solid-state imaging device 100 shown in FIG. 2,
although spontaneous polarization film 204 is formed directly on
light receiving sections 202 of semiconductor substrate 201,
spontaneous polarization film 204 can be formed via insulation film
301 so long as it is formed on light receiving sections 202, as in
solid-state imaging device 150 shown in FIG. 3. That is, as shown
in FIG. 3, insulation film 301 may be formed on semiconductor
substrate 201 on light receiving sections 202, and spontaneous
polarization film 204 may be formed on insulation film 301.
Insulation film 301 can be formed for example from SiO.sub.2 film,
SiN film, SiON film and the like.
[0073] In solid-state imaging device 150 shown in FIG. 3, holes are
induced at an interface with insulation film 301 of light receiving
sections 202 by spontaneous polarization film 204 having
polarization. Accordingly, the hole accumulation layer is formed on
the light receiving surface side of light receiving sections 202.
Thus, similar to solid-state imaging device 100 shown in FIG. 2,
noise charges generated at the interface level can be reduced, and
the dark current can be suppressed. Further, similarly, since
spontaneous polarization film 204 can easily be deposited uniformly
with respect to the respective pixels, there is no variation among
the pixels, and the dark current can also be suppressed.
[0074] In solid-state imaging devices 100 and 150 shown in FIG. 2
and FIG. 3, spontaneous polarization film 204 preferably has an
orientation of its polarization in the same direction from first
surface 201a of semiconductor substrate 201 to second surface 201b.
That is, it is preferable for the orientation to be in a direction
vertical to a main surface of semiconductor substrate 201 and that
extends from the side on which wiring layer 203 of semiconductor
substrate 201 is formed to the side on which the light is
incident.
[0075] As described above, by configuring the orientation of the
polarization of spontaneous polarization film 204 to be in the
direction from first surface 201a to second surface 201b, the
orientation of the polarization is indicated by a vector of the
polarization from a negative charge side to a positive charge side.
Accordingly, negative charges can be formed on the side of light
receiving sections 202 of spontaneous polarization film 204, and
positive charges can be accumulated on the light incident side of
spontaneous polarization film 204. Thus, the hole accumulation
layer can be formed on the interface of the light receiving surface
of light receiving sections 202 uniformly without any variation
among the pixels, and the dark current can be suppressed
effectively.
[0076] Further, in solid-state imaging devices 100 and 150 shown in
FIG. 2 and FIG. 3, spontaneous polarization film 204 is preferably
of a material in which a crystal is oriented.
[0077] Thus, by configuring the material of spontaneous
polarization film 204 as the material in which the crystal is
oriented, the polarization can be maintained according to the
crystal being oriented. Accordingly, the change in an amount of the
polarization in the spontaneous polarization film caused by the
manufacturing processes such as the water treatment and heat
treatment can be almost eliminated. Thus, since a stable hole
accumulation layer which is less susceptible to outside influences
can be formed on the interface of light receiving sections 202
uniformly without any variation among the pixels, the dark current
can be suppressed effectively. Here, as the material in which the
crystal is oriented, for example, it may be any one selected from
among ZnO (zinc oxide), GaN (gallium nitride), AlN (aluminum
nitride), SrTiO.sub.3 (strontium titanate), Pb(Zr, Ti)O.sub.3 (lead
zirconate titanate), SrBi.sub.2Ta.sub.2O.sub.9 (strontium bismuth
tantalate), (Bi, La) .sub.4Ti.sub.3O.sub.12 (lanthanum bismuth
titanate), BaTiO.sub.3 (barium titanate), BiFeO.sub.3 (ferric acid
bismuth), and Ba.sub.xSr.sub.(1-x)TiO.sub.3BST (solid solution of
barium titanate and strontium titanate).
[0078] Since spontaneous polarization film 204 formed by the above
material has a large amount of spontaneous polarization, a further
stabilized hole accumulation layer can be formed, and the dark
current can be suppressed even more effectively.
[0079] Note that, spontaneous polarization film 204 formed using
the above material can be formed by performing deposition of the
above material by using sputtering, sol-gel method, electron beam
vapor deposition method, and the like. Further, during formation of
spontaneous polarization film 204 or after the formation of
spontaneous polarization film 204, the amount of polarization of
spontaneous polarization film 204 can be increased by performing a
process to increase crystalline such as high-temperature
processing.
[0080] Further, the component selected from the above materials is
preferably deposited under 400.degree. C. or less. Accordingly,
since the material in which the crystal is oriented can be formed
after having formed the wirings, the manufacturing process can be
simplified.
[0081] As an example, a case of having formed spontaneous
polarization film 204 with ZnO will be described. FIG. 4 is a
diagram schematically showing a crystal structure of ZnO. As shown
in FIG. 4, ZnO has a Wurz structure, and an upward spontaneous
polarization vector (direction of arrow A) is indicated by the
orientation of Zn atoms and O atoms. A concentration of a charge
amount of the spontaneous polarization of ZnO is about 5
(.mu.C/cm.sup.2), so that the number of holes induced on light
receiving sections 202 by this spontaneous polarization of ZnO is
about 3.times.10.sup.13 (piece/cm.sup.2). Thus, a stable and
sufficient hole accumulation layer can be formed on light receiving
sections 202, and the dark current can be suppressed as
desired.
[0082] Note that, in the case where the material in which the
crystal is oriented is ZnO, the conductivity of ZnO is preferably
p-type. Accordingly, a potential at a junction portion of ZnO and
Si of semiconductor substrate 201 comes to be in a structure in
which the holes are easily accumulated, and the dark current can be
suppressed effectively. Further, in the case where the material in
which the crystal is oriented is ZnO, the oxygen defect
concentration of the ZnO is preferably 1.times.10.sup.17
(piece/cm.sup.3) or less. Accordingly, the potential at the
junction portion of ZnO and Si of semiconductor substrate 201 comes
to be in a structure in which the holes are easily accumulated, and
the dark current can be suppressed effectively.
[0083] Further, in solid-state imaging devices 100 and 150 shown in
FIG. 2 and FIG. 3, spontaneous polarization film 204 may be made of
an organic material having polarization, and polarized charges of
the organic material may be generated in the direction of film
growth of the organic material by the orientation of the organic
material.
[0084] By configuring spontaneous polarization film 204 as above,
since spontaneous polarization film 204 can be formed at low-
temperature, the amount of the spontaneous polarization can be
increased. Thus, the hole accumulation layer that is sufficient to
suppress the dark current can be formed.
[0085] Such spontaneous polarization film 204 can be formed by
using fluoropolymer.
[0086] As an example, a case of having formed spontaneous
polarization film 204 with a PVDF (polyvinylidene fluoride) that is
the fluoropolymer will be described. FIG. 5 is a diagram
schematically showing a molecular chain structure of the PVDF. As
shown in FIG. 5, since the PVDF is a low molecular material formed
of a low molecular mass body having (--CH.sub.2CF.sub.2--) as a
monomer unit, thermal decomposition of molecular chains is unlikely
to occur, and mixing of the impurities is rare. Accordingly, the
deposition for example using a method, such as the vacuum
deposition method, by which the control of the film thickness and
orientation can be performed relatively easily becomes possible.
Thus, as in the solid-state imaging device of the present
embodiment, it is especially suitable for the manufacture of the
backside-illumination-type solid-state imaging device that performs
formation of the spontaneous polarization film after having formed
the wiring layer. A concentration of a charge amount of the
spontaneous polarization of PVDF is about 13 (.mu.C/cm.sup.2), so
that the number of holes induced on light receiving sections by
this spontaneous polarization of PVDF is about 1.times.10.sup.14
(piece/cm.sup.2). Thus, a sufficient hole accumulation layer can be
formed, and the dark current can be suppressed as desired.
SECOND EXEMPLARY EMBODIMENT
[0087] Next, solid-state imaging device 200 of the second exemplary
embodiment of the present invention will be described with
reference to FIG. 6. FIG. 6 is a diagram schematically showing a
cross section of pixels in solid-state imaging device 200 of the
second exemplary embodiment of the present invention.
[0088] Note that, an overall configuration of solid-state imaging
device 200 of the second exemplary embodiment of the present
invention is similar to that of solid-state imaging device 100 of
the first exemplary embodiment of the present invention shown in
FIG. 1, and therefore a description thereof will be omitted.
Further, a basic configuration of the pixel of solid-state imaging
device 200 of the second exemplary embodiment of the present
invention shown in FIG. 6 is similar to that of solid-state imaging
device 100 of the first exemplary embodiment of the present
invention shown in FIG. 2, and therefore a description thereof will
be omitted. Thus, in FIG. 6, same reference numbers are given to
identical constitutional components to those shown in FIG. 2, and
their description is either simplified or omitted, and
configurations of characteristic sections will be described in
detail.
[0089] As shown in FIG. 6, solid-state imaging device 200 of the
second exemplary embodiment of the present invention has a
configuration in which spontaneous polarization film 204 is
sandwiched between hydrogen barrier films 601 and 602 formed of
SiN. That is, as shown in FIG. 6, this configuration has hydrogen
barrier film 601 formed at least on the light receiving surface of
light receiving sections 202 of semiconductor substrate 201,
spontaneous polarization film 204 formed on this hydrogen barrier
film 601, and further hydrogen barrier film 602 formed on
spontaneous polarization film 204.
[0090] As described above, by having the configuration of
sandwiching spontaneous polarization film 204 between hydrogen
barrier films 601 and 602, an amount of the spontaneous
polarization of spontaneous polarization film 204 can be suppressed
from being decreased in the manufacturing process such as water
treatment and hydrogen annealing.
[0091] Thus, in solid-state imaging device 200 of the second
exemplary embodiment of the present invention, a more stabilized
hole accumulation layer can be formed uniformly over the entirety
of the imaging region on the side of the surface on which light is
incident of light receiving sections 202 than in solid-state
imaging device 100 of the first exemplary embodiment of the present
invention. Accordingly, noise charges generated in the interface
level can be reduced uniformly without any variation among the
pixels, and the dark current can be suppressed uniformly at the
entirety of the imaging region.
[0092] Note that, in the present embodiment, although hydrogen
barrier films 601 and 602 are formed by SiN films, they may be
formed by any one selected from among TiN film, Al.sub.2O.sub.3
film, TiAlO film, TaAlO film, TiSiO film, and TaSiO film.
[0093] Further, the material selected from the above materials is
preferably deposited under 400.degree. C. or less. Accordingly,
since the material in which the crystal is oriented can be formed
after having formed the wirings, the manufacturing process can be
simplified.
[0094] Further, in the present embodiment, although hydrogen
barrier films 601 and 602 are formed above and under spontaneous
polarization film 204 in a manner of sandwiching spontaneous
polarization film 204, hydrogen barrier film 602 may be formed only
on an upper side of spontaneous polarization film 204 so as to
cover spontaneous polarization film 204 from the upper side (side
from which the light is incident). Note that, in the case of having
formed hydrogen barrier film 602 only on the upper side of
spontaneous polarization film 204, it is preferable to form an
insulation film (not shown) formed of SiN film and the like between
light receiving sections 202 of semiconductor substrate 201 and
spontaneous polarization film 204.
THIRD EXEMPLARY EMBODIMENT
[0095] Next, solid-state imaging device 300 of a third exemplary
embodiment of the present invention will be described with
reference to FIG. 7. FIG. 7 is a diagram schematically showing a
cross section of pixels in solid-state imaging device 300 of the
third exemplary embodiment of the present invention.
[0096] Note that, an overall configuration of solid-state imaging
device 300 of the third exemplary embodiment of the present
invention is similar to that of solid-state imaging device 100 of
the first exemplary embodiment of the present invention shown in
FIG. 1, and therefore a description thereof will be omitted.
Further, a basic configuration of the pixel of solid-state imaging
device 300 of the third exemplary embodiment of the present
invention shown in FIG. 7 is similar to that of solid-state imaging
device 100 of the first exemplary embodiment of the present
invention shown in FIG. 2. Thus, in FIG. 7, same reference numbers
are given to identical constitutional components to those shown in
FIG. 2, and their description is either simplified or omitted, and
configurations of characteristic sections will be described in
detail.
[0097] As shown in FIG. 7, solid-state imaging device 300 of the
third exemplary embodiment of the present invention has a
configuration in which spontaneous polarization film 204 is formed
by laminating two layers of spontaneous polarization films. That
is, as shown in FIG. 7, in the present embodiment, spontaneous
polarization film 204 includes first spontaneous polarization film
204a formed at least on the light receiving surface of light
receiving sections 202 of semiconductor substrate 201, and second
spontaneous polarization film 204b formed on first spontaneous
polarization film 204a. Note that, although spontaneous
polarization film 204 has a two-layer structure in the solid-state
imaging device shown in FIG. 7, spontaneous polarization film 204
may be formed of two or more plural layers.
[0098] Accordingly, by configuring spontaneous polarization film
204 with plural layers, the hole accumulation layer that is uniform
and sufficient can be formed on the light receiving sections of the
pixels in an entire imaging region, compared to the case of
configuring spontaneous polarization film 204 by a single layer.
Thus, the dark current can be efficiently suppressed without any
variation among pixels.
[0099] This is because by forming spontaneous polarization film 204
in plural layers, the occurrence of a region in which the hole
accumulation layer cannot be formed sufficiently due to an
interface of grains formed by spontaneous polarization film 204 can
be reduced. Hereinbelow, this point will be described in
detail.
[0100] The grains (grain boundary) is a region in which crystal is
intermittently formed, and in the interface of the grains of the
spontaneous polarization film, the effect of the spontaneous
polarization is small, so that the hole accumulation layer cannot
be formed sufficiently. Accordingly, if a boundary of the grains is
formed on the light receiving sections, the concentration of the
hole accumulation layer caused by spontaneous polarization vary
among the pixels, so that the dark current cannot be controlled
uniformly. However, as in the present embodiment, if the
spontaneous polarization film has a laminate structure with two or
more layers, even if the boundary of the grains is formed in the
first layer of spontaneous polarization film, the second layer of
spontaneous polarization film is formed on this boundary of the
grains in the first layer of spontaneous polarization film, and the
hole accumulation layer is formed by the second layer of
spontaneous polarization film; thus, the case with the spontaneous
polarization film having two layers has lower possibility that the
region in which the hole accumulation layer cannot be formed
sufficiently due to the interface of grains being present, compared
to the case of the spontaneous polarization film being a single
layer. Thus, a sufficient hole accumulation layer can be formed as
the number of layers of the spontaneous polarization film is
increased.
[0101] Accordingly, in solid-state imaging device 300 of the third
exemplary embodiment of the present invention, by configuring
spontaneous polarization film 204 with the laminated structure of
plural layers, the occurrence of the region in which the hole
accumulation layer cannot be formed sufficiently due to the
interface of the grains formed in spontaneous polarization film 204
can be reduced, and the concentration of hole accumulation layer
induced by spontaneous polarization film 204 can be made uniform
among the pixels over the entirety of the imaging region. Thus, the
dark current can be suppressed uniformly without any variation
among pixels. Note that, spontaneous polarization film 204 can
remove the variation among the pixels as the number of the
spontaneous polarization film to be laminated increases, and the
uniformity in the formation of the hole accumulation layer over an
entirety of the imaging region can be improved.
[0102] As described above, in the present embodiment, although the
film configuring the plural layers of spontaneous polarization
films is configured by the same material, the same effect can be
achieved even in forming the above films by different materials.
Examples of the material of the films configuring the plural layers
of spontaneous polarization film 204 include ZnO, GaN, AlN,
SrTiO.sub.3, Pb(Zr,Ti)O.sub.3, SrBi.sub.2Ta.sub.2O.sub.9,
(Bi,La).sub.4Ti.sub.3O.sub.12, BaTiO.sub.3, BiFeO.sub.3 and
Ba.sub.xSr.sub.(1-x)TiO.sub.3, and the film may be configured by
selecting one of the above or may be configured by combining plural
types of the above.
[0103] As above, the solid-state imaging device of the present
invention has been described based on the respective embodiments,
however, the solid-state imaging device of the present invention is
not limited to these embodiments. Further, characteristic
configurations described in the solid-state imaging device of each
embodiment can be adapted to one another. For example, the hydrogen
barrier film in the solid-state imaging device of the second
exemplary embodiment of the present invention may be adapted to the
solid-state imaging device of the third exemplary embodiment of the
present invention. Further, respective constitutional components in
the plurality of embodiments may be combined as desired without
departing from the spirit and scope of the present invention;
further, various modifications that would be conceived by those
skilled in the art without departing from the spirit and scope of
the present invention are also included in the scope of the present
invention.
[0104] Further, the solid-state imaging device of the embodiment of
the present invention has the feature in peripheral configuration
of the light receiving sections that performs photoelectric
conversion, and as a circuit configuration, a circuit configuration
of a typical MOS type solid-state imaging device can be adapted.
Further, as for the manufacturing process of bonding the supporting
substrate and removing the substrate, a manufacturing process for a
typical backside-illumination-type solid-state imaging device can
be adapted.
[0105] Note that, in the present description, "solid-state imaging
device" refers to a device including photoelectric conversion
elements provided on a semiconductor chip, and that is for
outputting the image signals to outside; and "imaging device"
refers to an imaging apparatus having the solid-state imaging
device, such as a digital still camera, digital video camera, cell
phone camera, surveillance camera.
[0106] The solid-state imaging device of the present invention is
useful for various types of imaging devices with a function to take
a picture, such as the digital still cameras, cell phones, video
cameras, surveillance cameras.
* * * * *